Injection laser

ABSTRACT

An injection laser comprises a laser heterostructure, at least one radiation inflow region adjoining the laser heterostructure, and reflectors that together form an optical resonator. The laser heterostructure comprises an active layer, cladding layers, and ohmic contacts. The radiation inflow region adjoining the laser heterostructure is transparent to the laser radiation and is located on at least one side of the active layer. The radiation inflow region additionally includes at least one optical facet, an outer surface, and an inner surface. Radiation generated in the active layer flows into the radiation inflow region and exits the laser.

RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/718,017, filed on Feb. 9, 2001, which is acontinuation-in-part of International Application No. PCT/RU99/00275filed at the Russian Receiving Office on Aug. 5, 1999, published in alanguage other than English under PCT Article 21(2) as WO 00/10235 onFeb. 24, 2000. Accordingly, priority under §365(c) is claimed toInternational Application No. PCT/RU99/00275 filed Aug. 5, 1999.Additionally, priority under §119 is claimed to Russian PatentApplication No. 98114581 (now U.S. Pat. No. 2,142,665) filed Aug. 10,1998.

FIELD OF THE INVENTION

[0002] The invention relates to quantum electronic technology, and morespecifically to efficient semiconductor sources of radiation with anarrow radiation patterns.

BACKGROUND OF THE INVENTION

[0003] The injection laser (hereinafter referred to as “the laser”) is adevice that converts electrical energy into the light possessing anarrow spectral composition and high directivity.

[0004] Different types of lasers are known: lasers with a strip-typeactive lasing region and with radiation output through the mirror of anoptical resonator (S. S. Ou et. al., Electronics Letters (1992), Vol.28, No. 25, pp. 2345-2346), distributed-feedback lasers (Handbook ofSemiconductor Lasers and Photonic Integrated Circuits, edited by Y.Suematsu and A. R. Adams, Chapman-Hill, London, 1994, pp. 44-45 and393-417), laser amplifiers, including a master oscillator poweramplifier (MOPA) (IEEE J. of Quantum Electronics (1993), Vol. 29, No. 6,pp. 2052-2057), and lasers with curved resonators and radiation outputthrough a surface (Electronics Letters (1992), Vol. 28, No. 21, pp.3011-3012). Further expansion of the applications of such lasers isimpeded by insufficiently high output power, efficiency, operating life,and reliability, including situations with monomode lasing.

[0005] The laser described in U.S. Pat. No. 4,063,189, issued to D. R.Scifres et al. in 1977 includes a laser heterostructure (hereinafterreferred to as a “heterostructure”) that contains an active layer ofGaAs positioned between two optically homogeneous cladding layers. Thegain region of the operating laser, of length L_(GR), in practicecoincides with the thick active layer into which non-equilibriumcarriers are injected by means of ohmic contacts. As the term isconventionally employed, a gain region is that part of theheterostructure which includes the active layer and from which radiationis spreading in a activated laser. The gain region, hereinafter referredto as “the GR”, is the medium of the optical resonator. The length ofthe GR along the longitudinal gain axis is bounded by flat end surfacesthat act as reflectors. The length L_(OR) of the optical resonator(Fabry-Perot) coincides with the length L_(GR), so that the ratio

μ=L _(OR) /L _(GR)   (1)

[0006] is equal to one. Reflective coatings with a coefficient ofreflection close to one (hereinafter referred to as “reflectivecoating”) are applied to the reflectors of the optical resonator. Theradiation inflow region (hereinafter referred to as “RIR”), as which asubstrate of GaAs is used, borders on a surface of one of the claddinglayers that is distant from the active layer. The inner surface of theRIR, whose area is equal to the area of the GR, is located on thecladding layer adjacent to the RIR. The flat optical facets of the RIRare a continuation of the planes of the reflectors of the opticalresonator and are perpendicular to the longitudinal gain axis of the GR.A coating with a reflection coefficient close to zero (hereinafterreferred to as “antireflective coating”) is applied to one of theoptical facets (hereinafter referred to as “the facet”), while areflective coating is applied to the other facet. The facet with theapplied anti-reflective coating is the output surface. The RIR is madeelectrically conductive, and an ohmic contact is made with its outersurface, which is opposite the inner surface. Another ohmic contact ismade from the direction of the heterostructure.

[0007] When direct current is supplied to the laser, nonequilibriumcarriers are injected into the active layer, and induce the generationof radiation of a specified wavelength λ and mode composition in themedium of the optical resonator. Part of the laser radiation from the GRexits the laser through the RIR. The angle of outflow of radiation isdefine by the following equation:

φ=arccos(n _(eff) /n _(RIR))   (2)

[0008] (see J. K. Buttler et al., IEEE Journ. of Quant. Electron.(1975), Vol. QE-11, p. 402). Note that the use of identical compositionsfor the active layer and RIR (both made of GaAs) restricted the range ofratios n_(eff)/n_(RIR) from more than 0.9986 to 1, and the outflow angleφ to the range from 3° to 0°, respectively.

[0009] The following basic parameters were obtained for the fabricatedlaser (see D. R. Scifres et al., U.S. Pat. No. 4,063,189, 1977, as wellas D. R. Scifres et al., Applied Physics Letters (1976), Vol. 29, No. 1,pp. 23-25): a threshold current density j_(thr) of 7.7 kA/cm², athreshold current J_(thr) of 7.0 A for a length L_(OR) of 400 μm, ashort-pulse output power of 3 W, a differential efficiency on the orderof 35-40%, and an angle of divergence Θ₁ of 2° in the vertical plane forlaser radiation output through the face. The vertical plane referred tois the plane that passes through the longitudinal gain axis and that isperpendicular to the active layer. The corresponding horizontal plane isperpendicular to the vertical plane.

SUMMARY OF THE INVENTION

[0010] An injection laser comprising at least one gain region having alongitudinal gain axis and outputting laser radiation at an outflowangle φ comprises a laser heterostructure, at least one radiation inflowregion adjoining the laser heterostructure, and reflectors that togetherform an optical resonator. The laser heterostructure comprises an activelayer, which forms at least one of the gain regions, cladding layerscomprising at least one layer having a refractive index, and ohmiccontacts. The radiation inflow region adjoining the laserheterostructure is transparent to the laser radiation, has a refractiveindex n_(RIR), and is located on at least one side of the active layer.The radiation inflow region additionally includes at least one opticalfacet, an outer surface, and an inner surface, the optical facet beingoriented at an angle of inclination ψ with respect to a planeperpendicular to the longitudinal gain axis. At least part of theoptical resonator coincides with at least part of the radiation inflowregion and at least part of the gain region. The laser heterostructureand the adjoining radiation inflow region together have an effectiverefractive index n_(eff) such that

[0011] n_(RIR) exceeds n_(eff),

[0012] arccos(n_(eff)/n_(RIR))≦arccos(n_(eff-min)/n_(RIR)), and

[0013] n_(eff-min) is greater than n_(min),

[0014] where n_(eff-min) is the minimum value of n_(eff) for laserheterostructures with radiation inflow regions that produce outflow ofradiation from the active layer into the radiation inflow region, andn_(min) is the smallest of the refractive indices in the cladding layersof the heterostructure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIGS. 1-7 schematically depict longitudinal sections (along theoptical gain axis of the GR) of different designs of lasers with GR endsurfaces made in the form of planes that extend the planes of thecorresponding facets of the RIR, and with one-way radiation output.

[0016] Specifically, in FIGS. 1-3, the facets of the RIR are implementedas reflectors of the optical resonator;

[0017] in FIG. 1, the laser has two inclined facets all shown with apositive angle of inclination ψ equal to φ;

[0018] in FIG. 2, the laser includes an external reflector in the formof a plane mirror to one of the inclined facets; and

[0019] in FIG. 3, the laser has one facet with an angle of inclination ψequal to zero;

[0020] FIGS. 4-7 depict lasers wherein parts of the outer surface of theRIR that are implemented as reflectors of the resonator;

[0021] in FIG. 4, the laser has two inclined facets of the RIR withnegative angles of inclination ψ equal to (π/4−φ/2),

[0022] in FIG. 5, the laser has an external reflector in the form of adiffraction grating to one of the inclined facets;

[0023] in FIG. 6, the laser has a facet with an angle of inclination ψequal to zero; and

[0024] in FIG. 7, the laser has one inclined facet of the RIR with apositive angle of inclination and another inclined facet with a negativeangle of inclination.

[0025] FIGS. 8-9 schematically depict longitudinal sections of designswith parts of the outer surface of the heterostructure that areimplemented as reflectors of the optical resonator;

[0026] in FIG. 8, the laser has two inclined facets with angles ofinclination ψ equal to (π/4+φ/2); and

[0027] in FIG. 9, the laser has one inclined facet with an angle ofinclination ψ equal to (π/4+φ/2), and the other with an angle ofinclination ψ equal to zero.

[0028]FIG. 10 schematically depicts a longitudinal section of the designof a laser with two facets with angles of inclination ψ equal to zero,and with outer inclined reflectors in the form of plane mirrors.

[0029] FIGS. 11-13 schematically depict cross-sections of lasers withohmic contacts positioned differently with respect to the RIR;

[0030] in FIG. 11, the ohmic contact is on the outer surface of the RIR;

[0031] in FIG. 12, the ohmic contact is located on the electricallyconductive sublayer of the cladding layer adjacent to the RIR; and

[0032] in FIG. 13—the ohmic contact is on the electrically conductivepart (layer) of the RIR adjacent to the heterostructure.

[0033] FIGS. 14-15 schematically depict a longitudinal section (FIG. 14)and perpendicular cross-section (FIG. 15) of the lasers with six GRsthat are galvanically series-parallel connected and have a single commonRIR.

[0034] FIGS. 16-18 schematically depict longitudinal sections, and FIG.19 depicts a perpendicular cross-section of the laser with amultiplicity of GRs independently galvanically controllable, withseparate RIRs for three different sequences of GR;

[0035] in FIG. 16, each laser has two inclined facets on the RIR withpositive angles of inclination (see FIG. 9) and the output of laserradiation is in the direction perpendicular to the plane of the activelayer;

[0036] in FIG. 17, each laser has one inclined facet forming part of theoptical resonator with a positive angle of inclination and a secondinclined facet with a negative angle of inclination (see FIG. 8) and theoutput of laser radiation is in the direction perpendicular to the planeof the active layer; and

[0037] in FIG. 18—each laser has two inclined facets on the RIR withpositive angles of inclination (see FIG. 1) and the output of laserradiation is at an angle φ with respect to the plane of the activelayer.

[0038] FIGS. 20-21 schematically depict longitudinal sections of thelaser, with GRs that are galvanically series connected and that aredisposed along their own gain axes and to a separate RIR;

[0039] in FIG. 20, the three GRs is on one surface of the RIR; and

[0040] in FIG. 21, the placement of four GRs is on two opposite surfacesof the RIR.

[0041]FIG. 22 schematically depicts the longitudinal section of thelaser with two inclined facets and three GRs with a different thicknessof the cladding layer for the middle GR and the end GRs.

[0042]FIG. 23 schematically depicts the longitudinal section of thelaser with two inclined facets and three GRs with an identical thicknessof the cladding layer for the middle GR and the end GRs.

[0043]FIG. 24 schematically depicts the longitudinal section of thelaser in the shape of a rectangular parallelepiped with one thin-layerRIR and three GRs and with a different thickness of the cladding layerfor the middle GR and the end GRs.

[0044]FIG. 25 schematically depicts the longitudinal section of thelaser in the shape of a rectangular parallelepiped with two thin-layersRIR on both sides of the active layer and with an identical thickness ofthe cladding layer for the middle GR and the end GRs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0045] Embodiments of the invention will now be described with referenceto the accompanying Figures, wherein like numerals refer to likeelements throughout. The terminology used in the description presentedherein is not intended to be interpreted in any limited or restrictivemanner, simply because it is being utilized in conjunction with adetailed description of certain specific embodiments of the invention.Furthermore, embodiments of the invention may include several novelfeatures, no single one of which is solely responsible for its desirableattributes or which is essential to practicing the inventions hereindescribed.

[0046] One preferred embodiment of the invention comprises a laser witha lower current-density threshold, increased differential efficiency,reduced astigmatism and angles of divergence of the output radiation inthe vertical and horizontal planes. This laser possesses enhancedspectral characteristics of the laser radiation, an expanded range ofdirection of laser-radiation output, and increased effective length ofthe optical resonator. In the aggregate, the result is increased power,efficiency, operating life, and reliability. This laser may comprise amultibeam laser. Note also that the technology for fabricating thislaser is simplified.

[0047] The laser comprises an injection laser which includes a laserheterostructure that contains an active layer and cladding layers, inwhich it is possible to form a gain region. The laser also includesreflectors, which form an optical resonator, ohmic contacts, and on atleast one side of the active layer a radiation inflow region (RIR) whoseinner surface borders on the corresponding cladding layer. The conditionfor radiation outflow from the active layer into the radiation inflowregion is fulfilled if the refractive index n_(RIR) of the radiationinflow region exceeds the effective refractive index n_(eff) for theaggregate consisting of the laser heterostructure and the adjoiningradiation inflow region. This condition is fulfilled whenarccos(n_(eff)/n_(RIR)) is greater than zero. Accordingly, thecomposition and thicknesses of the active layer, cladding layers, andRIR are selected so that the condition for outflow of radiation from theactive layer into the RIR is fulfilled, i.e., that the refractive indexn_(RIR) of the RIR exceeds the effective refractive index n_(eff) of theheterostructure and of RIR 7 or φ=arccos(n_(eff)/n_(RIR))>0. At leastpart of the medium of the optical resonator is made of at least part ofthe inflow region and of at least part of the gain region. At least oneof the reflectors of the optical cavity is made with a reflectioncoefficient selected from the range greater than zero and less than one.Lasing occurs during operation of this injection laser which includes atleast one inflow region transparent to laser radiation produced by thelaser. In addition, from at least one part, the at least one gain regionformed is characterized by a gain G_(outflow) (cm⁻¹) of outflowingradiation from the active layer into the inflow region, the latter beingcharacterized by an introduced threshold loss factor α_(RIR-thr) (cm⁻¹).The value of the gain G_(outflow) (cm⁻¹) is selected to be greater thanthe factor α_(RIR-thr) (cm⁻¹). The condition for radiation outflow fromthe active layer into the radiation inflow region is defined by therelations:

arccos(n _(eff) /n _(RIR))≦arccos(n _(eff-min) /n _(RIR)),

[0048] where n_(eff-min) is greater than n_(min), and where n_(eff-min)is the minimum value of n_(eff) out of all possible n_(eff) for themultiplicity of laser heterostructures with radiation inflow regionsthat are of practical value. The index n_(min) is the smallest of therefractive indices in the heterostructure cladding layers.

[0049] The laser is unique in its choice of the medium for the opticalresonator, which includes at least part of the RIR and at least part ofthe GR. Negative optical feedback is assured by the fact that at leastone of the reflectors in the optical resonator, which is disposed, forexample, on one of the facets of the RIR, is made with a reflectioncoefficient selected from the range greater than zero and less than one.The choice of the compositions, thicknesses, and number of layers andsublayers of the heterostructure and RIR in the working laser assuresoutflow of directional spontaneous radiation or emission from the activelayer (or GR) into the RIR with an intensity sufficient to fulfill thecondition for lasing in the optical resonator. For any laser as well asthis particular embodiment, a condition for lasing is that the radiationgain exceed the losses. This condition for operating the injection laserwill be realized, in terms introduced above, when the value of the gainG_(outflow) (cm⁻¹) of the outflowing radiation from the active layerinto the RIR exceeds the value of the threshold loss factor α_(RIR-thr)(cm⁻¹); this threshold loss factor α_(RIR-thr) characterizes theradiation inflow region and moreover all radiation losses in the opticalresonator at the lasing threshold. The lasing-threshold conditionobtained may be written as:

G _(outflow-thr)=α_(RIR-thr)=(μ·α_(RIR))+α_(out)+α_(diffr),   (3)

[0050] where G_(outflow-thr) (cm⁻¹) is the value of the gain G_(outflow)at the lasing threshold, α_(RIR) is the optical loss factor of the laserradiation in the RIR (which includes, e.g., absorption, scattering),α_(out) is the net loss factor, which is related to the laser radiationoutput from the optical resonator and which is equal to:

α_(out)=(2L _(GR))⁻¹·1n(R ₁ ·R ₂)⁻¹,   (4)

[0051] α_(diffr) is the coefficient of diffraction losses of laserradiation as it exits from the optical resonator. More specifically:

α_(diffr)=(L _(OR))⁻¹·1n{1−(λ·L _(OR) /n _(RIR) ·S _(refl))}⁻¹,   (5)

[0052] S_(refl) is the area of the reflectors of the optical cavity,L_(OR) is the length of the optical resonator, which is equal to(μ·L_(GR)) (see equation (1)), and R₁ and R₂ are the coefficients ofreflection for the reflectors of the optical resonator.

[0053] Depending on the laser, the ratio μ, equation (1), may range fromapproximately 0.8 to 3.0. The current density through the laser at whichequation (3) is fulfilled is the threshold current density j_(thr).

[0054] Note that the lasing preferably does not occur in the GR, which,in both the laser disclosed in U.S. Pat. No. 4,063,189, issued to D. F.Scifres et al. in 1977, as well as in other known lasers, corresponds tothe medium of the optical resonator. This objective is easilyaccomplished by selecting the mode of intensive outflow, in which thevalue of G_(outflow) (cm⁻¹) is selected to be close to the value of thetotal gain G_(GR) (cm⁻¹) of the radiation propagating in the GR. Or moreaccurately, the following condition is fulfilled: the difference betweenthe gains (G_(GR)−G_(outflow)) is smaller than the total loss factorα_(GR-thr) (cm⁻¹) of the radiation propagating in the GR. Moreover, theintensive outflow mode is preferable for the lasers, since it results inincreased efficiency. In addition to the mode of intense outflow ofradiation from the GR, the laser is also characterized as producing anoutflowing radiation mode having a wide range of outflow angles φ (seeequation (2)), and accordingly of the ratios (n_(eff)/n_(RIR)).Preferably, the upper bound of the outflow angles φ_(max) is defined bythe relations:

arccos(n _(eff) /n _(RIR))≦arccos(n _(eff-min) /n _(RIR))=φ_(max),   (6)

for n_(eff-min)>n_(min),   (7)

[0055] where n_(eff-min) is the minimum value of n_(eff) out of allpossible n_(eff) for the multiplicity of heterostructures with inflowregions that are of practical value, and n_(min) is the smallest of therefractive indices in the heterostructure cladding layers. Usingnumerical calculations for a heterostructure based on InGaAs/GaAs/AlGaAscompounds with a RIR of GaAs, which emits at wavelengths of betweenabout 0.92-1.16 μm, the maximum outflow angle φ_(max) was found to beapproximately 30°.

[0056] The laser with the aforementioned features is unique in that ituses spontaneous radiation directed at an angle to the longitudinal gainaxis in the GR, followed by amplification thereof and lasing in theoptical resonator. The path of the laser rays in such a resonatorexperiences a “bending” (“refraction”), with simultaneous amplificationof the radiation. The angle φ of radiation outflow from the gain regionin the RIR is made equal to the radiation inflow angle ξ for laser (andspontaneous) rays that are reflected from the reflectors of the opticalresonator and that are directed from the RIR back into the GR. Theaforementioned feature of optical-ray propagation is preferably used forall designs of the laser, based on the known optical principle of thereversibility of the ray path in optical systems, which is applied tothe multilayer laser heterostructure in aggregate with a RIR.

[0057] The aggregate of the characteristic features determines theuniqueness of the operation and the advantages of the lasers. Lasing andthe process of generation of the corresponding modes in their opticalresonator occur mostly as the laser rays propagate in the homogeneous,weakly absorbing volume of the RIR. Only after the laser rays reflectedfrom the facets of the RIR are incident on the heterostructure (whichgenerally is asymmetrical) does local amplification and total internalreflection occur. In conventional lasers the corresponding modes oflaser radiation are formed in a fundamentally different way, namelylasing occurs entirely in the thin active dielectric waveguide of a GRbounded by the end reflectors of the optical resonator, whileamplification occurs along the entire propagation path in the GR. Inview of the foregoing, the laser may be called an “injection laser (ordiode laser) with a resonant cavity.”

[0058] The aforementioned distinctions determine the basic advantages ofthe lasers. In comparison with conventional lasers, for example, thethreshold current density j_(thr) can be reduced. This feature is due tothe fact that if there are equal net losses to radiation output, definedby the factor α_(out) (see equation (4)), the optical losses in thevolume of a homogeneous RIR which are characterized by the coefficientμ·α_(RIR) (cm⁻¹), can be made smaller than the internal optical lossesin a multilayer gain region (the factor α_(GR)). This is possible, atleast in part, because the composition of the RIR may be selected todiffer from the composition of the semiconductor layers of theheterostructure. In addition, by selecting the Fresnel number N (whichis equal to λ·L_(OR)/n_(RIR)·S_(refl)) to be much larger than one, theknown diffraction losses can be made negligibly small (see equation(5)). Also see A. Meitland and M. Dann, Introduction to Laser Physics[in Russian], Nauka Publishers, 1978, pp.102-118.

[0059] There are additional possibilities for reducing the thresholdcurrent density in the lasers. This threshold current density is reducednot only in comparison with the threshold currents of a laser with asmall outflow angle φ (see U.S. Pat. No. 4,063,189, issued to D. R.Scifres et al. in 1977) but also in comparison with the thresholdcurrents of modern lasers with quantum-dimensional active layers, as forexample discussed in S. S. Ou et al. (Electronics Letters (1992), Vol.28, No. 25, pp. 2345-2346). One possibility is related to the selectionof larger outflow angles φ (from the range 0<φ<φ_(max)), which isdetermined by relations (2), (6), and (7) and results in an increase inthe optical radiation localization coefficient Γ, which in turninevitably leads to an additional decrease in the threshold currentdensities (see, e.g., T. M. CocKerill et al., Appl. Phys. Lett. (1991),Vol. 59, pp. 2694-2696).

[0060] The differential efficiency also can be increased with theselasers. The following estimating formula has been obtained tocharacterized this differential efficiency:

η_(d)=η₁·η₂.   (8)

[0061] Here, the coefficient η₁ corresponds to the efficiency of outputof the outgoing radiation from the GR into the RIR, and is equal to

η₁ =G _(outflow)/(G _(outflow)+α_(GR)).   (9)

[0062] In contrast, η₂ corresponds to the efficiency of output of thelaser radiation from the RIR, and is equal to

η₂=α_(out)/(α_(out)+(μ·α_(RIR))+α_(diffr)).   (10)

[0063] The factor α_(GR) includes of the optical radiation losses in theGR (the factor α_(GRF)) and the losses to radiation output at the startand end of the GR (the factor α_(GRO)). Specifically, α_(GR) is definedby the equation:

α_(GR)=α_(GRO)+α_(GRF).   (11)

[0064] By selecting a gain G_(outflow) significantly greater thanα_(GR), we will obtain an efficiency η₁ (see equation (9)) close to one.Note that in U.S. Pat. No. 4,063,189, issued to D. R. Scifres et al. in1977, the increase in the gain G_(outflow) is constrained by theincrease in the lasing threshold current. For the lasers designed asdescribed above, however, this constraint does not exist. If α_(out) isselected to be much larger from the sum (μ·α_(RIR))+α_(diffr), theefficiency η₂ can be made close to one (see equation (10)). Theefficiency η is defined, herein, as the total efficiency of the laserwithout regard for losses due to electrical resistance, for which thefollowing equation obtains:

η=η_(d)·η_(thr),   (12)

where

η_(thr)=(1−j _(thr) /j _(oper)),   (13)

[0065] and j_(oper) is the operating current density through the laser.It follows from relations (12) and (13) that simultaneously increasingη₁ and η₂ (equation (8)) and decreasing j_(thr) will lead to an increasein the efficiency η.

[0066] The spatial and spectral characteristics of the laser radiationcan also be improved in these laser devices. In the original design ofthe optical resonator, the mode of the laser radiation is basicallygenerated in the homogeneous volume of the RIR (or of homogeneous partsthereof) in the absence of nonequilibrium majority carriers. In ordinarylasers, the concentration of injected carriers and the optical gainaffect the value of the refractive index of the directional waveguidemodes of the radiation. This attribute significantly determines thestability or lack thereof of the spatial and spectral characteristics ofinjection lasers (M. Osinski et al., IEEE Journ. of Quant. Electronics,Vol. 23, 1987, pp. 9-29). In the lasers described above, however, theaforementioned gain and injection processes are distributed, and theyoccur only on a very small part of the total optical path length.Therefore, the lasing mode of one spatial mode with respect to thetransverse index in the direction parallel to the layers of the laserheterostructure (with a corresponding decrease in the angle ofdivergence Θ₂ in the horizontal plane) can be preserved forsignificantly larger dimensions of the strip than in ordinary lasers.Consequently, the divergence of the output radiation will besignificantly reduced in not only the vertical but also the horizontalplane. As defined herein, the horizontal plane corresponds to the planethat is perpendicular to the vertical plane and that is located on theoutput surfaces. In the general case, the output surfaces are defined asthe laser surface for radiation output.

[0067] Furthermore, stable generation of single-frequency laserradiation can be achieved in these lasers over a wider range ofcurrents. Moreover, the so-called “chirp effect,” the frequency shift ofthe laser radiation resulting from changes in the pumping-currentamplitude (see, e.g., T. L. Koch and J. E. Bowers, Electronics Letters,Vol. 20, 1984, pp. 1038-1039), which is undesirable for a number ofapplications, can also be reduced significantly.

[0068] Note also that the lasers described above have a feature thatsignificantly simplifies the technology for making them in comparisonwith conventional laser designs. For example, to eliminate undesirablelosses in the lasers disclosed in U.S. Pat. No. 4,063,189 issued to D.R. Scifres et al. in 1977, one reflector of the optical resonator mustbe made with a reflective coating, and the optical facet of the RIR thatis an extension thereof must be made, by contrast, with anantireflective coating. This design is difficult to fabricate in view ofthe micron dimensions of the reflector. Since the intensive outflow mode(G_(outflow)≅G_(GR)) is implemented for the lasers and since laserradiation is not generated in the GR, it is possible to simplify thetechnology for fabricating the lasers without significantly effectingthe output characteristics. This goal can be achieved by making theangles of inclination ψ and the reflection coefficients of the faces ofthe RIR and adjacent end surfaces the same.

[0069] Also in the lasers described above, the active layer ispreferably formed of at least one sublayer, and the active layer can beimplemented as one or several active sublayers, including sublayershaving quantum-dimensional thicknesses separated from each other bybarrier sublayers. The cladding layers, which are respectivelypositioned on the first surface and opposite second surface of theactive layer, are respectively formed from cladding sublayers I_(i) andII_(j), where i=1, 2, . . . , k and j=1, 2, . . . , m are defined asintegers that designate the sequential number of the cladding sublayers,counted from the active layer, with refractive indices n_(Ii) andn_(IIj), respectively, and with bandgaps E_(Ii) and E_(IIj). At leastone cladding sublayer is made in each cladding layer. If the activelayer comprises sublayers, the cladding layers generally are made of twoor more sublayers on each side of the active layer. For the case wherethe active layer comprises one sublayer with a thickness ofapproximately 50 nm or more, each cladding layer comprise one sublayer.We consider the gradient layers used (see, e.g., S. S. Ou et al.,Electronics Letters (1992), Vol. 2F, No. 25, pp. 2345-2346) to be thefinal number of sublayers of a cladding layer with corresponding n_(Ii)and n_(IIj) obtained by layering each sublayer in the gradient layer.Here, in general the refractive indices of the cladding layers usuallyare smaller than the refractive indices of the active sublayers. Byselecting the aforementioned versions of the active and cladding layers(for the specified heterostructure) it also is possible to effectimprovement of the efficiency and threshold current density, and toensure the necessary value of n_(eff) used in equations (2), (6), and(7).

[0070] In preferred embodiments, at least one of the angles ofinclination ψ of the facets of the RIR is greater than zero in absolutevalue as defined with respect to the plane perpendicular to thelongitudinal gain axis called the normal plane. The angle of inclinationψ is arbitrarily designated positive if the facet subtends an acuteangle with the inner surface (or with the active layer, since the outputsurface and the active layer are parallel to each other), and to benegative if the facet subtends an obtuse angle with the inner surface.The inclined facets introduced into the design and which have specifiedangles of inclination ψ make it possible, by using easy to implementtechnological solutions, to obtain an efficient design of an opticalresonator with negative feedback, that provides for different directionsof laser radiation output, as well. For some laser designs, barrierregions are introduced into the heterostructure. The introduction ofbarrier regions makes it possible to create lasers with a strip gainregion (i.e., in the form of a strip of width W_(GR)) that incur smalllosses of injection current to spreading. Barrier regions also enablemultibeam lasers to be formed.

[0071] To eliminate current losses, the length L_(RIR) of the innersurface of the RIR, which is determined along the longitudinal gain axisof the GR, and the width W_(RIR) of the RIR, are made to be at least oflength L_(GR) and at least of width W_(GR) of the GR, respectively. Thethickness d_(RIR) of the RIR depends on the outflow angle φ, the lengthL_(GR), and the angles of inclination of the optical facets. Thisthickness may be varied over a wide range from about 2 μm to about50,000 μm or more.

[0072] Since the RIR actually is the passive volume of the opticalresonator, transparency of the RIR is necessary for the functioning ofthe laser. To obtain higher efficiency of the laser, the RIR (or a partthereof) must be made of an optically homogeneous material, and theoptical radiation losses in it (to absorption and scattering) must bemuch smaller than the net losses to laser radiation output from theoptical resonator. Specifically, the condition α_(RIR)<<α_(out) must befulfilled, or

α_(RIR)<<(2μ·L _(GR))⁻¹·1n(R ₁ ·R ₂)⁻¹.   (14)

[0073] If the RIR is made of a semiconductor material, in addition tothe requirements of homogeneity, to fulfill equation (14) the RIR musthave a bandgap E_(RIR) larger than the bandgap E_(a) for the activelayer, which determines the wavelength λ of the laser radiation. Lossesto absorption are known to decrease approximately exponentially,depending on the difference between E_(RIR) and E_(a) (see, e.g., H. C.Huang et al., Journ. Appl. Phys. (1990), Vol. 67, No. 3, pp. 1497-1503).To reduce the optical loss factor α_(RIR) (cm⁻¹) and consequently toattain, in addition to high differential efficiency η_(d) and lowj_(thr), an increase in output radiation power (as a result of anincrease in the effective length of the optical resonator), it isdesirable for E_(RIR) to exceed E_(a) by at least about 0.09 eV. In thiscase the optical loss factor for absorption may reach values on theorder of about 0.1 cm⁻¹ or less. In the general case, the RIR may bemade not only of semiconductor materials. It is preferred that itscharacteristics, particularly the refractive index n_(RIR) and opticalloss factor α_(RIR) for absorption and scattering, satisfy the relationsin equations (2), (6), (7), and (14).

[0074] To simplify the technology for making the laser, the RIR maycomprise a substrate on which a heterostructure is grown. Furthermore,the RIR may be made electrically conductive, and in this case, an ohmiccontact is formed with the surface of the RIR.

[0075] In cases where the RIR is nonconductive, in order to obtain lowvalues of α_(RIR) (cm⁻¹) and increase the effective length L_(OR) of theoptical resonator and the output radiation power P (W), part of thevolume of the RIR that borders on the heterostructure is preferably madeelectrically conductive, and the remaining volume preferably comprises amaterial with an optical loss factor α_(RIR) of no more than about 0.1cm⁻¹. This part of the RIR that borders the heterostructure preferablyhas of a thickness no greater than W_(GR) (μm).

[0076] Hereinafter, this part of the volume of the RIR that borders onthe heterostructure and that has the specified thickness is referred toas the first layer of the RIR. The other parts of the RIR may be thesecond layer of the RIR, which is adjacent to the first, third, andsubsequent layers. Preferably, the parts of the RIR that are layersparallel to its inner surface comprise materials with differentrefractive indices. In such cases, when the difference in the propertiesof the aforementioned layers of the RIR includes not only electricalconductivity but also different refractive indices, the outflow angles φ(2) in the layers of the RIR can be controlled. Hence the thickness ofthe RIR and its layers also can be controlled. The outflow angle φ_(i)in the i-th layer (where i=2, 3, . . . , s are integers) with arefractive index n_(RIR) is equal to arccos(n_(eff)/n_(RIR)) (seeequation (2)). Therefore, if for example the refractive index n_(RIR1)of the first layer is smaller than n_(RIR2) for the second layer, thethickness of the second layer may be made smaller than for the firstlayer, and vice versa. Decreasing the thickness d_(RIR) may lead tosimplification of the technology and to a lowering of the costs ofmaking the RIR. In both cases, an ohmic contact is made with theelectrically conductive part of the RIR, and the thickness of this partof the RIR is preferably no greater than the width W_(GR) of the GR.

[0077] In lasers whose RIR has an optical loss factor α_(RIR) of no morethan about 0.1 cm⁻¹, it is possible to achieve a large volume of theactive GR (by increasing L_(GR) to approximately 1 cm) with smalllaser-radiation losses in the RIR, and to obtain large values of theoutput radiation power. In lasers having a width W_(GR) of microndimensions, to simplify the fabrication, an ohmic contact from thedirection of the RIR is made with one of the electrically conductivecladding sublayers that is located between the active layer and the RIR,preferably with the electrically conductive sublayer that has thesmallest bandgap.

[0078] For those laser designs in which, for large values of L_(GR), itis undesirable to have a large thickness d_(RIR) (μm), preferably atleast one of the cladding sublayers has a refractive index no smallerthan n_(RIR). This leads to an increase in the value of n_(eff) andconsequently to a decrease in the outflow angle φ (see equation (2)) andin d_(RIR). Small thicknesses d_(RIR) lead to savings of material in theRIR.

[0079] To simplify the technology for fabricating the lasers, preferablythe end surface of the GR, on at least one side has the same angle ofinclination ψ and the same reflection coefficient as the adjacentoptical facet of the RIR. As noted previously, in practice, this featurewill not degrade the performance of the laser.

[0080] Different embodiments of the injection laser are described below.

[0081] In one laser, for example, preferably at least one optical facetof the RIR comprises a reflector of the optical resonator and has apositive angle of inclination ψ equal to the outflow angle φ, which isequal to arccos(n_(eff)/n_(RIR)). This configuration provides theability to make the lasers with an outflow angle φ throughout the entirerange of its values, as defined in equations (2), (6), and (7), up toφ_(max). Within this range is included values of the angles φ largerthan the angle of total internal reflection σ. Hence, one can reduce thethreshold current density, increase the efficiency and power, decreasethe angle of divergence in the vertical plane, and effect output oflaser radiation through the optical facet of the RIR when the radiationis normally incident on the optical facet.

[0082] For the same purposes, but with implementation of laser radiationoutput perpendicular to the plane of the active layer, at least oneoptical facet is formed with a negative angle of inclination ψ equal to(π/4)−(φ/2), and at least part of the outer surface of the RIR comprisesa reflector of the optical resonator. This part of the outer surface ofthe RIR preferably corresponds at least to the portion where theprojection of the optical facet is formed on the RIR. Alternatively, atleast one optical facet of the RIR is formed with a positive angle ofinclination ψ equal to (π/4)+(φ/2), and at least part of the lasersurface opposite the RIR comprises a reflector of the optical resonator.This part of the laser surface opposite to the RIR preferablycorresponds at least to the portion where the projection of the opticalfacet is formed thereon. In the first case, radiation output will occurthrough the outer surface of the RIR, and in the second case it willoccur in the diametrically opposite direction.

[0083] In a number of other cases, in the aforementioned laser designsthe other optical facet of the RIR is formed with an angle ofinclination ψ of about zero. A reflective coating is formed on the otheroptical facet of the RIR (when the angle φ is less than the angle oftotal internal reflection σ on the output surface). This leads toone-way output of laser radiation, and also to a decrease in the lengthL_(GR) and in the angle of divergence Θ₁ of the output laser radiationin the vertical plane.

[0084] To enhance the spatial and spectral characteristics of the laser,preferably, at least one of the reflectors of the optical resonatorcomprises an external reflector. If the angle φ is smaller than theangle σ, the use of an external reflector (outside the RIR) makes itpossible to create a laser in which both facets of the RIR subtend anangle of inclination ψ equal to about zero. This simplifies thetechnology for fabricating the laser, since there is no need to make thefacets for the RIR sloped. In this case, negative feedback is generatedby using an external reflector (or reflectors) made with thecorresponding angle of inclination.

[0085] It is also possible that one of the reflectors of the opticalcavity, which is formed either as an external reflector, or on theoutput surfaces of the RIR or heterostructure, comprises a plane mirror,a cylindrical mirror, a spherical mirror, or a diffraction grating.

[0086] Note that it is accepted practice, see, e.g., I. I. Bronshteinand K. A. Semendyayev, Handbook of Mathematics (in Russian), p. 170,1953 to measure the angles of inclination ψ formed between twohalf-planes (a facet and the inner surface) as the angle between twoperpendiculars drawn in both half-planes from one point on the line oftheir intersection. The accuracy with which the angle of inclination ψis preferably made is determined by the dispersion angle of divergenceΔφ. The diffraction angle of divergence may be ignored because of itssmallness in comparison with the angle Δφ. The dispersion angle isdetermined instead by the spread of the outflow angle φ as a function ofthe wavelength λ, which varies over the range of the spectral band Δλfor spontaneous radiation. The angle Δφ has been determined by anumerical calculation using equation (2) for the known dependences ofn_(eff) and n_(RIR) on λ in the range Δλ. The calculations show that forthe most frequently used heterostructures with Δλ of about 20-50 nm, theangle Δφ lies in the range from about 0.5° to about 1.5°.

[0087] Preferred embodiments of the lasers include designs with two ormore, i.e., plurality of gain regions.

[0088] A unique feature of one multibeam laser is that at least two gainregions are formed on the inner surface of at least one RIR preferablyso as to produce identical outflow angles φ. The gain regions, which may(but not necessarily) have a rectangular shape, are positioned withspecified periods, including those in a mutually perpendiculardirection. In a number of cases, an independent ohmic contact is madewith each GR from the direction opposite the location of the RIR. Such alaser using an output reflector of the RIR will have a multiplicity oflaser beams, including beams that are spatially separated from eachother and that can be turned on independently by the operating current.

[0089] In another multibeam laser, a multiplicity of laser beams form atwo-dimensional matrix in which each beam is independently controllableby the operating current. The gain regions are formed from at least twosequences of GRs. In each at least two GRs are disposed so that the gainaxes of each GR in each sequence are parallel to each other. These gainaxes are positioned at a right angle to the line of intersection of theactive layer with the extension of the plane of the facet of the commonRIR for each sequence of GRs. Furthermore, from the direction of theRIR, on at least part of the outer surfaces of the common RIRs, ohmiccontacts and metallization layers electrically connected to them areformed. At least the metallization layers are formed in strips, one foreach sequence of GRs. From the direction opposite the location of theRIR, the metallization layers connected to the independent ohmiccontacts are formed in strips that are insulated from each other and arepositioned parallel to the gain axes of the GRs.

[0090] In another laser, several GRs are successively connected to aunified optical resonator. In this case, the GRs are formed along atleast one line parallel to the longitudinal gain axes of the GRs. Thespacing between the starts of the GRs is 2d_(RIR)/tan φ, and the outersurface is optically reflective, at least at points on the projection ofthe gain regions onto the outer surface at the outflow angle φ. It alsois possible to form at least one GR having identical outflow angles φ,on opposite surfaces, of RIRs along two lines that are parallel to eachother and to the longitudinal gain axes of the GRs; here, the shortestdistance between the starts of the GR on opposite sides of the RIR isselected to be d_(RIR)/sin φ. These modifications make it possible toincrease the radiation output power while at the same time reducing thethickness of the RIR and improving the conditions of heat removal.

[0091] In lasers with either one or a multiplicity of gain regions, thegain region or at least two adjacent GRs be galvanically isolated allthe way to the nonconductive part of the volume of the RIR, and that theohmic contacts of the gain regions be galvanically coupled by ametallization layer. This arrangement makes it possible to increase thevalue of the supply voltage and to perform effective matching of thelasers to power sources.

[0092] The laser described above includes an original design of anoptical resonator the volume (bulk) of whose medium comprises not onlyan active layer but also the volume of the gain region with intenseoutgoing radiation, as well as the passive volume of the radiationinflow region, which are formed with appropriately made compositions andthicknesses. These features along with the number of layers of the laserheterostructure, the configuration of the radiation inflow region andits optical facets, the ohmic contacts, and the metallization layers,make possible practical delimitation of the region of generation oflaser-radiation modes and the region of injection and stimulatedrecombination of nonequilibrium carriers.

[0093] This unique laser design offers many advantages. These include adecrease in the threshold current density, an increase in efficiency(including differential efficiency), and an improvement in the level ofastigmatism. This laser produces small angles of divergence close to thediffraction angles for two mutually perpendicular directions of outputradiation, and provides an increase in the stability of monomode lasing,a significant decrease in the dependence of the wavelength of thegenerated laser radiation on the pumping-current amplitude, and theability to increase the effective length of the optical resonator andradiation output power. Many of these advantages accrue from the uniquedesign of the laser and, in particular, by rejecting the traditionaldielectric waveguide design with an active layer inside, as a lasingmedium for generating directional waveguide modes. Additional advantagesof the laser include the ability to obtain different directions of laserradiation, including those perpendicular to the plane of the activelayer, as well as increased service life or lifetime and operationalreliability. These lasers are also highly manufacturable. An additionaladvantage of the laser with a multiplicity of gain regions is that theintegrated technology can be employed for fabricating these devices.

[0094] The technical implementation of the invention is based on knownbasic production processes, which by now are well developed and are usedextensively in laser manufacture. The range of radiation wavelengths ofthe lasers that have been put to use to date extends from the infraredto the ultraviolet. Depending on the wavelength, appropriateheterostructures are used for different sections of the wavelengthrange. For example, heterostructures based on semiconductor compounds inthe AlGaN/GaN/GaInN system, and also in the ZnCdSSe/GaAs system, aremost effective for ultraviolet, blue, and green radiation (0.36μm<λ<0.58 μm); compounds in the AlGaInP/GaAs system are most effectivefor red and yellow (0.58 μm<λ<0.69 μm); compounds in the AlGaAs/GaAssystem and in the InGaAs/GaAs/AlGaAs system are most effective forinfrared (0.77 μm<λ<1.2 μm); compounds in the GaInAsP/InP system aremost effective for infrared (1.2 μm<λ<2.0 μm); and compounds in theAlGaInSbAs/GaAs system are most effective for infrared (2.0 μm<λ<4.0μm). In each of the aforementioned ranges, appropriate materials for theRIR that satisfy conditions (2), (6), (7), and (14) must be selected,depending on the wavelength λ used and the heterostructure chosen. Amongsemiconductor materials for RIRs, preferred material include: GaN forthe AlGaN/GaN/GaInN system; ZnSe for the ZnCdSSe/GaAs system; GaP forthe AlGaInP/GaAs system; GaP for the AlGaAs/GaAs system; GaAs and GaPfor the InGaAs/GaAs/AlGaAs system; Si and GaAs for the GaInAsP/InPsystem; and Si and GaAs for the AlGaInSbAs/GaAs system. These laserdesigns can be successfully implemented by using the recently developed“wafer bonding” technology; see, e.g., H. Wada et al., IEEE Photon.Technol. Lett., Vol. 8, p. 173 (1996). The designs for efficientinjection lasers are applicable for at least all the foregoing ranges oflaser-radiation wavelengths and heterostructure systems.

[0095] With reference now to FIGS. 1 and 11, the preferred laser 1includes a heterostructure 2, which comprises an active layer 3positioned between two cladding layers 4 and 5, respectively, withsublayers I_(i) and II_(j) (not shown). Active layer 3 consists of twoactive sublayers and a barrier sublayer that separates them (not shownin FIG. 1). The length of the L_(GR) is about 4000 μm. The length of theoptical resonator L_(OR) is about 3760 [μm (see equation (1)), and theratio μ (equation (1)), is equal to about 0.9397. The width W_(GR) inthe form of a strip 30 (or mesa strip) bounded on the sides by barrierregions 6 is about 400 μm. The total width of the laser crystal is about1000 μm. A semiconductor RIR 7, bounded on the end faces by facets 8 and9, which are implemented as reflectors of the optical resonator, islocated on the surface, distant from active layer 3, of sublayer II_(m)of cladding layer 5. RIR 7 is implemented as a substrate 10 to which therequired form is imparted. Both facets of RIR 7, the first facet 8 andsecond facet 9, are inclined with a positive angle of inclination ψequal to the outflow angle φ, which is about 200. This angle ψ iscalculated from the normal plane, which is perpendicular to thelongitudinal gain axis in the GR. If the angle of inclination ψ ispositive, facets 8 and 9 subtend an acute angle with active layer 3. Areflective coating 11 with a reflection coefficient R₁ of about 0.999 isformed on the first facet 8, and a partially reflective coating 12 witha reflection coefficient R₂ of about 0.01 is formed on the second facet.The end surfaces 13, which determine the length of the gain regionL_(GR), are an extension of the corresponding planes of the inclinedfacets 8 and 9 and have the same inclinations and the same reflectioncoefficients as facets 8 and 9. This simplifies the fabricationtechnology. This simplification does not have any practical effect onthe parameters of laser 1, since strong outflow is realized in thepreferred laser 1, and there is practically no laser radiation throughend surfaces 13. The accuracy with which the facets 8 and 9 are inclinedmay range from about 19.6° to 20.4°. The thickness d_(RIR) of RIR 7, forwhich the relation

d _(RIR)≧(L _(RIR)·tan φ/(1+tan²φ)),   (15)

[0096] is fulfilled, is about 1,286 μm. Contact layer 14 is positionedon the surface of sublayer I_(k) of cladding layer 4, and an ohmiccontact 15 is formed on it. An ohmic contact 16 is made on the oppositeside of RIR 7, on its outer surface 17 of RIR 7 (in this case, on thesurface of substrate 10). Inner surface 18 borders on heterostructure 2,and is parallel to the plane of active layer 3.

[0097] Heterostructure 2, which comprises a number of semiconductorlayers and sublayers 19-27, together with contact layer 14, may be grownby the conventionally known method of Metal Organic Chemical VaporDeposition (MOCVD) on substrate 10 from electrically conductive galliumarsenide. The composition, thicknesses, refractive indices, type, dopingconcentrations, and absorption coefficients of layers 19-27 ofheterostructure 2, contact layer 14, and RIR 7 are presented in theTable. This heterostructure 2 also is used in the following embodiments(with the changes specified for the separate embodiments). The operatingwavelength for this heterostructure 2 is about 980 nm. In FIG. 1 and insubsequent FIGS. 2-10, 14, 16-18, and 20-25 conventional arrows show thedirections of propagation of laser radiation in RIR 7 and outside it.The laser 1 is mounted on a thermally conductive slab (not shown inFIGS. 1-25) against the side of ohmic contact 15. The power is suppliedto ohmic contacts 15 and 16.

[0098] The basic parameters for both the laser 1, and modifications ofit, were obtained by numerical modeling performed according to a programemploying a matrix method of solving Maxwell's equations with thecorresponding boundary conditions for the multilayer laserheterostructures (see, e.g., J. Chilwall and I. Hodkinson, Journ. Opt.Soc. Amer., A (1984), Vol. 1, No. 7, pp. 742-753). The calculationsemployed the following initial parameters: the material gain in activelayer 3 for achieving inversion was about 200 cm⁻¹, the proportionalityfactor between the gain and injected-electron concentration in activelayer 3 was about 5×10⁻¹⁶ cm², and the lifetime of the nonequilibriumelectrons in active layer 3 was 1 ns.

[0099] The calculations also assumed: an optical loss factor α_(GRO) inthe GR of about 3 cm⁻¹ (see, e.g., D. Z. Garbuzov et al., IEEE Journ. ofQuant. Electr. (1997), Vol. 33, No. 12, pp. 2266-2276) and inaccordance, for example, with H. C. Huang et al. (Journ. Appl. Phys.(1990), Vol. 67, No. 3, pp. 1497-1503), and with a value of the opticalloss factor α_(RIR) of the laser radiation in RIR 7 of about 0.1 cm⁻¹.The losses to output of spontaneous radiation through end surfaces 13 ofthe gain region were not taken into account in the calculations becauseof their smallness, so that α_(GR) (equation (11)), is about 3 cm⁻¹. Thevalues adopted for the parameters are typical of the laserheterostructure 2 in question, which is based on InGaAs/GaAs/AlGaAs. Fora heterostructure 2 using other compounds, such as GaInPAs/InP, theseparameters may change somewhat.

[0100] The following results were obtained by numerical calculation:

[0101] the threshold current density j_(thr) was determined to be about89.3 A/cm² (equation (3) is fulfilled for this current density);

[0102] the outflow angle φ is about 20°;

[0103] the dispersion angle of divergence Δφ for the outgoingspontaneous radiation (for the Δλ of 30 nm used in the calculation) wasfound to be about 0.8°;

[0104] the effective refractive index n_(eff) is about 3.3124;

[0105] the total gain G_(GR) and gain G_(outflow) for the outgoingradiation (reached for a current density j_(oper) of about 2,500 A/cm²through laser 1) are about 320.80 cm⁻¹ and 320.03 cm⁻¹, respectively;here the difference (G_(GR)−G_(outflow)), which is about 0.73 cm⁻¹, issmaller than α_(GR) (equation (11)), which is about 3 cm⁻¹, which meansthat the mode of intensive outflow has been selected, and that lasingdid not occur in the GR;

[0106] the net loss factor α_(out) (equation (4)), for the output laserradiation from RIR 7 is about 11.515 cm⁻¹;

[0107] the optical loss factor, defined as μ·α_(RIR), is about 0.09397cm⁻¹;

[0108] the threshold loss factor μ·α_(RIR-thr) (equation (3)), in RIR 7,defined as the sum (α_(out)+(μ·α_(RIR))+(60 _(diffr)), is equal to about11.609, and the α_(diffr) calculated from equation (5) is negligiblysmall;

[0109] the area of the gain region S_(GR) is about 1.6×10⁻² cm²;

[0110] the threshold current J_(thr), defined as (j_(thr)·S_(GR)), isabout 0.8 A;

[0111] the differential efficiency η_(d) is about 0.9827 (see equation(8)), and its components η₁ (equation (9)) and η₂ (equation (10)) areabout 0.9907 and 0.9919, respectively; and

[0112] the threshold loss factor η_(thr) (equation (13)) for a j_(oper)of about 2,500 A/cm² is 0.9643, and the efficiency η (equation (12)) oflaser 1 is 0.9476.

[0113] The output power P (W) of laser radiation is determined as:

P=η·J·(hv),   (16)

[0114] where J is the operating current through the device, equal toabout 40 A, and (hv) is the photon energy in volts, equal to about 1.265V. The value obtained for P is about 47.95 W. The radiation near-fieldarea (output aperture) S_(ap), defined as (d_(ap)·W_(GR)), is equal toabout 0.51×10⁻² cm², where d_(ap) is equal to L_(GR)·sin φ, specifically1,368 μm, and W_(GR) is approximately 400 μm. The angles of divergenceΘ₁ and Θ₂ of the output radiation were respectively estimated as thewavelength λ, divided by d_(ap), and the wavelength λ, divided byW_(GR). In the vertical plane, the angle Θ₁ was found to be about 0.72mrad. In the horizontal plane the angle Θ₂ is about 2.45 mrad for therange of currents for which monomode lasing can be maintained. Theoutput of laser radiation on the output facet 9, defined as P/S_(ap), isabout 9,402 W/cm².

[0115] Another embodiment of laser 1 (see FIG. 2) differs from the onedescribed above with regard to FIG. 1 in that an antireflective coating28 was applied to facet 8, and outer reflector 29 was implemented as aplane mirror measuring approximately 2,500×2,500 μm², with a reflectioncoefficient of about 0.999, which was parallel to facet 8 andapproximately 10,000 μm from it. The width W_(GR) was 1,368 μm, and thetotal width of the laser crystal was approximately 3,000 μm. The basicparameters of laser 1 in this embodiment that differ from the firstembodiment are: S_(GR), J_(thr), J_(oper), P (equation (16)), and S_(ap)are respectively equal to about 5.47×10⁻² cm², 1.43 A, 136.75 A, 163.9W, and 1.87×10⁻² cm², and Θ₁ and Θ₂ are identical and are equal toapproximately 0.72 mrad.

[0116] The difference between the laser depicted in FIGS. 10 and 11 andthe one shown in FIG. 3 is that facets 8 and 9 of RIR 7 were made withan angle of inclination ψ of zero. As a result of the increase in thethicknesses of layers 21 and 25 of heterostructure 2 (see Table), theoutflow angle φ was reduced to approximately 12°, which is smaller thanthe angle σ. Here, the plane of external reflectors 29 for providingnegative feedback was adjusted with an angle of inclination relative tothe normal plane of about 42.3°, and the angle Δφ was about 1.4°. Laser1 had unidirectional radiation output, since one reflector had areflective coating 11 with R₁ of about 0.999, and the other had acoating 12 with R₂ of about 0.05. In addition to the known advantagesinherent in lasers with external resonators (such as, the enhancement ofspatial and spectral characteristics), another advantage is simplifiedfabrication.

[0117] The laser 1 of FIG. 4 and FIG. 11 differed from the last shown inFIG. 1 in that both facets 8 and 9 of RIR 7 have a negative angle ofinclination ψ equal to (π/4−φ/2), specifically 35°. The length L_(RIR)is approximately 1,000 μm and the width W_(GR) is approximately 340 μm.The thickness d_(RIR) of RIR 7 is about 500 μm, and its length L_(ORIR)is about 1,700 μm. A reflective coating 11 with a reflection coefficientR₁ of about 0.999 is formed on the outer surface 17 at the location ofthe projection of facet 8 onto it, and a partially reflective coating 12with a reflection coefficient R₂ of approximately 0.02 is formed at thepoint of the projection of the other facet 9. The length L_(OR) of theoptical resonator, defined as μ·L_(GR) (equation (1)), is about 1,940μm, and the ratio μ equals 1.94. The following parameters were obtainedfor this laser 1:

[0118] the threshold current density j_(thr) is about 42 A/cm²;

[0119] the loss factors α_(out) and μ·α_(RIR) are about 3.913 cm⁻¹ and0.194 cm⁻¹, respectively;

[0120] the α_(diffr) calculated from equation (5) is negligibly small,and consequently α_(RIR-thr) (equation (3)) is about 4.107 cm⁻¹;

[0121] the efficiencies η₁, η₂, η_(d), η_(thr), and η are respectively0.9907, 0.958, 0.9439, 0.9832, and 0.9280;

[0122] the threshold current J_(thr) is about 0.143 A for an S_(GR) ofabout 0.34×10⁻² cm²; and

[0123] the operating current J_(oper) is approximately 8.5 A (for aj_(oper) of 2500 A/cm²), and the output power P (equation (16)) of laser1 under conditions of a single spatial mode is about 9.98 W, while theangles of divergence Θ₁ and Θ₂ are identical and are equal to about 2.8mrad.

[0124] The laser 1 depicted in FIGS. 5 and 11 differs from the one inFIG. 4 in that one of the reflectors of the optical resonator isexternal and is implemented as a reflective diffraction grating 29. Thisgrating enables single-frequency lasing.

[0125] In laser 1 shown in FIGS. 8 and 11 both facets 8 and 9 areinclined at a positive angle ψ equal to (π/4+φ/2), specifically about55°, and the output radiation is directed at a right angle to the planeof active layer 3 in the direction toward the heterostructure 2. The GR,of width about 15.3 μm and length 45 μm, is located in the middle ofinner surface 18, whose width W_(IRIR) is about 25 μm and whose lengthL_(IRIR) is about 135 μm. Coatings 11 and 12, whose reflectioncoefficients are about 0.999 and 0.90, respectively, are applied to theinner surface 18 at the points of projection of facets 8 and 9. Abarrier region 6 is formed on the remaining area of inner surface 18,which is free of heterostructure 2 and coatings 11 and 12. The thicknessof RIR 7 is 23 μm, the length of the outer surface 17 is about 73.8 μm,and the length L_(OR) of the optical resonator was about 129 μm. Theaforementioned design changes determined the following parameters:j_(thr) is about 125 A/cm², and α_(out), α_(diffr), μ, and (μ·α_(RIR))are respectively about 11.7 cm⁻¹, 4.22 cm⁻¹, 2.86, and 0.286 cm⁻¹, andconsequently α_(RIR-thr) is about 16.2 cm⁻¹. The threshold current J isabout 0.861 mA, the operating current J_(oper) is about 13.8 mA, theoutput power P (equation (16)) of the laser radiation is about 11.66 mW,and η_(d) (equation (8)) and η (equation (12)) are about 0.7139 and0.6693, respectively. This laser 1 generates in a single longitudinalmode, its wavelength is practically independent of the pumping currentover a wide range thereof, and the angles of divergence Θ₁ and Θ₂ areidentical and are equal to 6.4 mrad (0.37°). This laser, in addition tothe others (see FIGS. 4 and 6-9) is competitive with conventional lasershaving vertical resonator (see, e.g., B. Weigl et al., ElectronicsLetters, Vol. 32, No. 19, pp. 1784-1786, 1996).

[0126] The laser 1 depicted in FIGS. 7 and 11 differs from those shownin FIGS. 10, 4, and 8 in that the facets 8 and 9 are made different insign but identical in absolute value of the angle of inclination ψ,which is approximately 30°. This design makes it possible to obtainoutput radiation directed at a right angle to the plane of active layer3, but for smaller values of the ratio μ, see, e.g., equation (1), thanfor some of the lasers described above.

[0127] What is common to the lasers 1 in FIGS. 3, 6, and 9 is that facet8 of RIR 7 is made with an angle of inclination ψ of about zero. For thelasers 1 made in accordance with the design in FIGS. 1, 4, and 8, thisconfiguration leads to a doubling of the linear size of the radiationoutput aperture, with a corresponding decrease in the angle ofdivergence Θ₁ in the vertical plane, provided that the lengths L_(GR)are kept the same.

[0128] In the lasers shown in FIGS. 1-10, mesa strip 30, whichdetermines the dimensions of the GR, may be made of a specified width byusing barrier regions 6 (see FIGS. 11-13). For a laser 1 with a mesastrip 30 with a width of micron size, ohmic contact 16 can be made, forexample, with sublayer 25 of cladding layer 5, as shown in FIG. 12. Inthis case, RIR 7 may be an insulating region, which facilitates theselection of RIR 7 with a small coefficient α_(RIR). If a two-layer RIR7 comprising a first electrically conductive layer 31 and a secondinsulating layer 32 is present, ohmic contact 16 is made with the firstlayer 31 (FIG. 13). In this case, the second layer 32 of RIR 7 may benot only an insulating layer, but also a layer that differs incomposition from first layer 31, which also facilitates the selection ofboth small values of α_(RIR2) and corresponding thicknesses d_(RIR2) oflayer 32, provided that the refractive index of the layers of RIR 7 areselected appropriately.

[0129] The lasers 1 in FIGS. 14-21 differ from the ones described abovein that their designs include two or more (i.e., a multiplicity of) gainregions. A characteristic feature of the multibeam laser 1 shown inFIGS. 14 and 15 is that 32×30 GRs are disposed on the inner surface 18of RIR 7 and are series and parallel electrically coupled to togetherfor the passage of the operating current therethrough. The length andwidth of each GR are approximately 290 and 85 μm, respectively. They arearranged in the form of a rectangular grating whose spacings along (x)and across (y) the length L_(IRIR) of the RIR are approximately 300 and100 μm, respectively. The length L_(IRIR) and width W_(IRIR) of theinner surface 18 of RIR 7 are approximately 9,600 and 3,000 μm,respectively, the thickness of RIR 7 is 3,214 μm, the length L_(OR) ofthe optical resonator is approximately 10,216 μm, and the reflectioncoefficients of coatings 11 and 12 on facets 8 and 9 are about 0.999 and0.32, respectively. The basic parameters for the laser beams from eachGR, j_(thr), α_(out), μ, and (μ·α_(RIR)), have values of about 182A/cm², 19.95 cm⁻¹, 35.2, and 3.52 cm⁻¹, respectively, and consequentlyα_(RIR-thr) is about 23.47 cm⁻¹; the threshold current J_(thr) is about43.7 mA, the operating current J_(oper) is selected to be approximately600 mA, and the output power of laser monomode radiation P (equation(16)) is about 592.6 mW. Here, η_(d) (equation (8)) is 0.8421, and η(equation (12)) is about 0.7808, and the angles of divergence Θ₁ and Θ₂are about 9.0 mrad and 8.28 mrad, respectively.

[0130] Thirty GRs, which are in each of 32 rows of the grating that arepositioned across the length of the RIR, are electrically interconnectedin series, and the rows themselves are connected in parallel. Thegalvanic series coupling of the aforementioned GRs is implemented (seeFIG. 15 and FIG. 14) by introducing an electrically conductive firstlayer 31 (with a carrier concentration of approximately 10¹⁸ cm⁻³) ofRIR 7, an insulating region 35 of width 15 μm, metallization layers 36to ohmic contacts 15, connecting ohmic contacts 15 of two such adjacentGRs, between which is an insulating region 35 that borders (in contrastto barrier region 6) on the insulating region with layer 32 of RIR 7(see FIG. 15). The aforementioned metallization layers 36, which alsoprovide a parallel current connection of the aforementioned 32 rows ofGRs, are implemented as 16 lines approximately 180 μm wide and 9,600 μmlong. In the working device, to each GR there will correspond aradiation near field and an output laser beam on the reflector with apartially reflective coating 12. If the dimensions, the length of theoptical resonator and the length of the GR itself are chosen properly,they will not overlap (see FIG. 14). The total operating current throughlaser 1 is about 3.2 A for an operating voltage of 48 V (1.6 V for eachGR), and the total output power of all laser beams is about 568.9 W.

[0131] A characteristic feature of the lasers 1 depicted in FIGS. 16-19is that a common RIR 7 with common facets 8and 9 is formed for a linearsequence (or linear array) of GRs. The line of intersection of the planeof the active layer with the extension of the planes of facets 8 and 9subtends a right angle with the gain axes of the gain regions in theaforementioned linear array. The device may contain a fairly largenumber of such linear arrays, which are monolithically joined byheterostructure 2 with barrier regions 6, which is common to all thelinear arrays. A separate laser beam will correspond to each GR in eachsuch line of GRs. The direction of radiation output from such multibeamlasers 1, with a multiplicity of separate GRs, may be eitherperpendicular to the plane of active layer 3 (see FIGS. 16 and 17) or atan angle φ (see FIG. 18). In contrast to lasers 1 in FIGS. 14 and 15,the thickness of RIR 7 in lasers 1 FIGS. 16-19 may be reducedsignificantly, and the density of the laser beams per square centimetermay be significantly increased.

[0132] In the laser 1 depicted in FIGS. 16 and 19, 32 linear sequencesor array of GRs, each of which contains 30 GRs that have the samedimensions and parameters as the laser 1 in FIGS. 8 and 11, are made onthe inner surfaces 18 of the 32 RIRs 7. With the exception of its widthof approximately 750 μm, RIR 7 has the same dimensions andcharacteristics as the laser 1 in FIGS. 8 and 11. On each of four sides,the GRs are current separated by barrier regions 6, and an independentohmic contact 15 with contact layer 14 is made by known methods. Thespacing of the GRs in the line is about 25 μm, and the spacing betweenlines is about 135 μm. For independent supply of operating current toeach GR, 30 longitudinal strips of metallization layers 36 are made toohmic contacts 15, and 32 transverse strips of metallization layers 37,which are directed transverse to the optical gain axes of the GRs, areformed to the ohmic contacts 16 of each of the 32 RIRs. When anelectrical signal is supplied to an arbitrary combination of twomutually perpendicular metallization strips 36 and 37, the laser beam isgenerated with the involvement of that GR which is disposed betweenintersecting strips 36 and 37 of the selected metallization strips. Eachlaser beam (of which there are 960 in all) has the same parameters as inthe laser 1 in FIGS. 9 and 11.

[0133] The laser 1 shown in FIGS. 20 and 21 include several GRs that areconnected in series, one after another, into a common optical resonator.This is accomplished by virtue of reflections from the outer opticalsurface 17 of RIR 7 (see FIG. 20) and by virtue of reflections, withcorresponding gain in laser radiation from gain regions disposed on bothsurfaces of RIR 7 (see FIG. 21). These embodiments provide an increasedeffective length of the optical resonator for smaller thicknesses of RIR7, including situations with large outflow angles φ. Furthermore, inthem conditions more conducive to heat removal are provided as a resultof the distributed nature of the heat sources in the gain regions.

[0134] Note also that for the laser 1 described with reference to FIGS.14-21, certain electrical connections of the longitudinal and transversestrips of metallization layers 36 and 37 can be used to obtain series,parallel, or series-parallel galvanic coupling of the gain regions. Thisdesign makes it possible to perform more effective matching ofhigh-power multibeam lasers to power sources.

[0135] The following laser 1, unlike the ones described above inconnection with FIG. 20, has one strip-type GR with length L_(GR) andwidth W_(GR). The RIR 7 is in the form of a rectangular parallelepipedand includes one layer with a thickness d_(RIR) that is located abovethe lower contact layer 14 (which may be necessary, depending on thematerials employed in the laser 1). The other ohmic contact 16 (with thecorresponding metallization layers) is located on the outer opticsurface 17, except on portions of the outer surface of the RIR where thestrip-type GR is projected onto this outer surface. The reflectors ofthe optical resonator are disposed on optical facets of the RIR. Thesize of the optical facets 8, 9 is at least equal to the product of thethickness d_(RIR) and the width W_(GR).

[0136] In another embodiment of the laser 1, the entire outer surface 17of the RIR 7 is covered with a semiconductive layer with a refractiveindex smaller than n_(eff). The outer surface 17 of the RIR 7 may, forexample, be covered with a material having a refractive index equal ton_(min), i.e., the lowest refractive index of the semiconductivematerials of the cladding layers 4 and 5 of heterostructure 2.Preferably, the contact semiconductive layer 14 (if necessary) has aband gap smaller than that of the semiconductor layer on the outersurface 17 of the RIR 7. The ohmic contact 16 is located above thissemiconductor layer on the outer surface having index n_(min).

[0137] In yet another embodiment of the laser 1, the region of injectionor region of gain comprises a portion that starts out as a rectangularstrip about 2 to 5 μm in width and from about 0.5 to several millimetersin length but which widens to form a funnel-shaped injection region. Thefunnel shaped region is flared at an ranging from about 5° to 15° over alength which may range from about 0.5 to 2 mm or more. Such aconfiguration enables the reduction of the threshold currents of laser1, leading to the further increase in its efficiency. In addition, thisconfiguration allows for the significant reduction of the angle ofdivergence θ₂ of laser radiation in the horizontal plane at the exit ofthe funnel.

[0138] A laser is also possible having an RIR 7 on both sides of theactive layer 3 of the heterostructure 2.

[0139] In these four embodiments described above, as well as in thelaser 1 depicted in FIG. 20, wherein a semiconductor is disposed on theouter surface 17 of the RIR 7, the radiation flows into the RIR 7approximately in the form of two flat waves directed at outflow angles φin two opposite directions, see, e.g., equation (2). In addition, if thethickness d_(RIR) is smaller than L_(IRIR) multiplied by tanφ, a portionof the outflowing radiation would, after falling on the semiconductorlayer of the outer surface 17 of the RIR with an index n_(min) becompletely reflected from it. Subsequently, the reflected radiation willreturn to the GR of the heterostructure 2 where it is re-radiated backinto the RIR 7. Once in the RIR 7, the light will be totally internallyreflected from the semiconductor layer with an index n_(min) once again.This process will continue to repeat itself. The number of suchradiation re-reflections is determined mainly by the value of the angleφ, determined by equation (2), the thickness d_(RIR) of RIR 7, and thelength, L_(GR), of the injection region.

[0140] The resulting radiation into the RIR 7 will be directedapproximately along the respective perpendiculars to the reflectors ofthe optical resonator of the laser 1. These reflectors are located onthe optical facets of the RIR 7 through which laser radiation willprimarily be emitted.

[0141] The shape and size of the near-field radiation pattern of thelaser 1 at on the optical facets of the RIR 7 will be restricted by thesize of the rectangular facets, one of the sides of which is slightlygreater than the thickness d_(RIR), the other side being slightlygreater than the width W of the strip of the injection region.Accordingly, the angle of divergence Θ₁ in the vertical plane may beestimated as approximately equal to the wavelength λ of the radiationdivided by the thickness d_(RIR) of the RIR 7. By selecting thethickness d_(RIR), it is possible to reduce the angle of divergence Θ₁as well as the density of radiation, which is important for obtaininghigh output power and a high reliability for the Laser 1. This thicknessd_(RIR) preferably ranges from about 2 to 100 μm and in certain casesmay be smaller than about 2 μm.

[0142] It is also important to note that, with respect to theembodiments of Laser 1 described above, as a result of the reduction ofthe thickness d_(RIR) of RIR 7, it is not necessary to rely on waferbonding technology. In contrast, the heterostructure 2, along with theRIR 7, the semiconductor layer with index n_(min) formed thereon, aswell as the contact layer 14 may be deposited in the single process ofepitaxial growth. This approach simplifies the manufacturing process andenables less expensive manufacturing equipment to be employed tofabricate a variety of laser which operate at different wavelengths λ.

[0143] The laser depicted in FIGS. 22 and 11, in contrast to the onesdescribed above with regard to FIGS. 1 and 11 has three strip-type gainregions (GR), a middle GR surrounded by two end GRs with contacts 14 atthe end of the cladding layer 4. The thickness d_(RIR) of RIR 7 has beenselected to be at least as large as the value of thickness d_(RIR) byformula (15) where L_(IRIR) is replaced by the length of the end GRdesignated hereinafter as L_(GRE). The thickness of the cladding layer 5of the middle GR is greater than the thickness of the end GRs, forexample, the thickness of the layer 5 in the middle GR may be equal tothe thickness of layer 4 as shown in FIG. 22. In an operating laser 1,at the current densities discussed above, the intensity of outgoingradiation in the end GRs is significantly greater than the intensity ofoutgoing radiation in the middle GR, where it is practically nil. As aresult of this phenomenon, stimulated (super-luminescent) radiation of asufficient power is introduced from the middle GR to the end GRs. Thisstimulated (super-luminescent) radiation enables electrical powerintroduced into the end GRs to be converted into a directed radiation ina highly efficient process which generates laser radiation. Thisgeneration occurs in the optical resonator which includes the middle andend GRs, as well as a portion of the RIR 7. The reflectors of theoptical resonator comprise one optical facet 8 having a reflectivecoating 11 thereon and the other optical facet 9 with a partiallyreflective coating 12 adhere thereto. This design advantageously has alow threshold current density j_(thr), a high conversion efficiency η,and a thickness d_(RIR) of the RIR 7 that is small as compared to thethickness of the RIR in the laser 1 discussed above with regard to FIGS.1 and 11. Having a small thickness d_(RIR) allows for the growth of theRIR layer 7 by the methods of epitaxial growth, thereby simplifying theprocess of manufacture.

[0144] The laser 1 shown in FIGS. 23 and 11 differs from that of FIG. 22in that an identical single-layer RIR 7 and an identical cladding layer5 are associated with all three GRs, the middle and two ends.Nevertheless, the current density in the middle GR of the operatinglaser 1 has a value that allows for super-luminescent radiation flowingfrom the middle GR into the end GRs to be much higher than the radiationoutgoing from the middle GR. The selection of heterostructures achievingthese requirements was made by employing numerical methods.

[0145] Another embodiment of the laser 1 (not shown) is similar to thelaser shown in FIG. 22 except that the contact layer 14 and the ohmic 15are continuous. This design produces equal current densities through themiddle and end GRs and advantageously offers simplicity of operation.

[0146] Note that these design features extend to the laser 1 depicted inFIGS. 2-10 and 14-19, and 20-21 as well as to the laser of FIG. 1.

[0147] The laser 1 depicted in FIGS. 24 and 11, unlike the laser 1 inFIG. 22, has an RIR 7 shaped as a rectangular parallelepiped with asmall thickness d_(RIR), which preferably ranges from about 2 to about10 μm. This thickness can be much smaller than the length of the end GR,L_(GRE), multiplied by tanφ. A semiconductive layer 38 with a refractionfactor n_(min) is located on the outer surface 17 of the RIR 7 similarto the one described above. The construction of the RIR 7 and thefunctioning of the semiconductor layer formed on the outer surface 17 ofthe RIR are similar to those described above in connection for examplewith the laser 1 of FIG. 20. The design of FIG. 24 advantageouslyreduces the generation threshold and increases efficiency.

[0148] The laser 1 depicted in FIG. 25 differs because it contains twooutflow regions 7 located on both sides of the active layer 3 which likethe RIR in the laser of FIG. 24 comprises relatively thin layers. Thetwo outflow regions 7 also have associated therewith adjacentsemiconductive layers 38. In this embodiment, the layers of RIR 7 andcladding layers 5 are identical for all three GRs. Functionally, thisembodiment is similar to the laser 1 depicted in FIG. 23; in theoperating laser 1, the current density in the middle GR is greater thanin the end GRs.

[0149] In addition to the embodiments described above, lasers 1 with twoGRs could be also be used, the first of these GRs being similar inconstruction to the middle GR, while the second one being similar to theend GR. While the first GR preferably comprises the strip-type, thesecond one can preferably is funnel-shaped, widening from the strip ofthe first GR.

[0150] Thus, in the lasers 1 described herein, the output power of thelaser radiation is increased manifold, the threshold current densitiesare reduced significantly and the angles of divergence in two mutuallyperpendicular directions are reduced, the effective lengths of opticalresonators are increased, near-maximum values of the efficiencies(including the differential efficiency) are attained, and the dependenceof the generated wavelength of the laser radiation on thepumping-current amplitude is reduced significantly. High-efficiencylasers with output of laser beams, including output in the directionperpendicular to the plane of the active layer, and multibeam lasers,including those turned on independently, also are obtained.

[0151] In general injection lasers are used in fiber-opticcommunications and data-transmission systems, in ultra-high-speedoptical computing and switching systems, in the design of medicalequipment, laser process equipment, and frequency-doubled lasers, andfor the pumping of solid-state and fiber lasers. Accordingly, theinjection lasers described above can be advantageously employed in thesevarious application as well as numerous others.

[0152] Moreover, the present invention may be embodied in other specificforms without departing from the essential characteristics as describedherein. The embodiments described above are to be considered in allrespects as illustrative only and not restrictive in any manner. Thescope of any invention is, therefore, indicated by the following claimsrather than the foregoing description. Any and all changes which comewithin the meaning and range of equivalency of the claims are to beconsidered in their scope. TABLE Names & Nos. of layers, Thickness ofCarrier Absorption sublayers, Composition layer Refractive Type ofconcentration coefficient & regions of layer d (μm) index n conductionN_(e) (cm⁻³) α (cm⁻¹) 1 2 3 4 5 6 7 Contact layer 14  GaAs 0.3 3.525 P 2× 10¹⁹ 140 Cladding layer, 4 19 Al_(0.6)Ga_(0.4)As 0.9 3.20 P 1 × 10¹⁸7.0 sublayers 20 Al_(0.6)Ga_(0.4)As 0.6 3.20 P 2 × 10¹⁷ 3.50 21 GaAs0.06 3.525 — — 3.0 Active layer, 3 22 In_(0.2)Ga_(0.8)As 0.008 3.63 — —3.0 sublayers 23 GaAs 0.012 3.525 — — 3.0 24 In_(0.2)Ga_(0.8)As 0.0083.63 — — 3.0 Cladding layer, 5 25 GaAs 0.06 3.525 — — 3.0 sublayers 26Al_(0.6)Ga_(0.4)As 0.1 3.20 N 5 × 10¹⁷ 2.0 27 Al_(0.6)Ga_(0.4)As 0.253.20 N 1 × 10¹⁸ 3.0 Radiation inflow 7 GaAs 1286.0 3.525 N 1 × 10¹⁸ 0.1region

What is claimed is:
 1. An injection laser comprising at least one gainregion having a longitudinal gain axis and outputting laser radiation atan outflow angle φ, said injection laser comprising: a laserheterostructure comprising: an active layer forming said at least onegain region; cladding layers comprising at least one layer having arefractive index, and ohmic contacts; and at least one radiation inflowregion adjoining said laser heterostructure that is transparent to saidlaser radiation, has a refractive index n_(RIR), and is located on atleast one side of said active layer, said radiation inflow regionincluding at least one optical facet, an outer surface, and an innersurface, said optical facet being oriented at an angle of inclination ψwith respect to a plane perpendicular to said longitudinal gain axis;and reflectors that together form an optical resonator at least part ofwhich coincides with at least part of said radiation inflow region andat least part of said gain region, wherein said laser heterostructureand said adjoining radiation inflow region together have an effectiverefractive index n_(eff) such that n_(RIR) exceeds n_(eff);arccos(n_(eff)/n_(RIR))≦arccos(n_(eff-min)/n_(RIR)); and n_(eff-min) isgreater than n_(min), where n_(eff-min) is the minimum value of n_(eff)for laser heterostructures with radiation inflow regions that produceoutflow of radiation from the active layer into the radiation inflowregion, and n_(min) is the smallest of the refractive indices in thecladding layers of the heterostructure.
 2. The injection laser of claim1, wherein said active layer comprises at least one sublayer.
 3. Theinjection laser of claim 2, wherein said cladding layers arerespectively disposed on a first surface and on an opposite secondsurface of said active layer and comprise cladding sublayers I_(i) andII_(j), respectively, with refractive indices n_(Ii) and n_(IIi) andbandgaps E_(Ii) and E_(IIi), respectively, where i=1, 2, . . . , k andj=1, 2, . . . , m are defined as integers that designate the sequentialnumbers of the cladding sublayers counted from the active layer with atleast one cladding sublayer within each cladding layer.
 4. The injectionlaser of claim 3, wherein at least one of said cladding sublayersdisposed between said active layer and said radiation inflow region iselectrically conductive and has an ohmic contact formed therewith. 5.The injection laser of claim 4, wherein at least two of said claddingsublayers disposed between said active layer and said radiation inflowregion comprise electrically conducting semiconductors having bandgapsof varying sizes, said ohmic contact being formed with said sublayerhaving the smallest bandgap.
 6. The injection laser of claim 3, whereinthat at least one of said cladding sublayers has a refractive index atleast as large as the refractive index n_(RIR) of said radiation inflowregion.
 7. The injection laser of claim 1, wherein said at least oneoptical facet is oriented so as to subtend an acute angle with the innersurface.
 8. The injection laser of claim 1, wherein said laserheterostructure includes barrier regions.
 9. The injection laser ofclaim 1, wherein said gain region comprises a strip-type gain region.10. The injection laser of claim 1, wherein: said gain region has alength L_(GR) and a width W_(GR); and said inner surface of theradiation inflow region has a length L_(RIR) and a width W_(RIR)respectively at least as large as the length L_(GR) and width W_(GR) ofsaid gain region.
 11. The injection laser of claim 10, wherein saidradiation inflow region includes a first portion having a thickness nogreater than W_(GR) that borders said laser heterostructure and iselectrically conductive, said radiation inflow region having a secondportion that comprises material having an optical loss factor α_(RIR) ofno more than about 0.1 cm⁻¹.
 12. The injection laser of claim 11,wherein an ohmic contact is formed with said electrically conductiveportion of said radiation inflow region.
 13. The injection laser ofclaim 1, wherein said radiation inflow region has a thickness rangingbetween about 2 to about 50,000 micrometers (μm).
 14. The injectionlaser of claim 1, wherein said radiation inflow region comprises anoptically homogeneous material.
 15. The injection laser of claim 14,wherein said radiation inflow region comprises a semiconductor having abandgap E_(RIR) (eV) and said active layer comprises a semiconductorhaving bandgap E_(a) (eV), said bandgap E_(RIR) (eV) exceeding saidbandgap E_(a) (eV) of the active layer by more than about 0.09 eV. 16.The injection laser of claim 1, wherein said radiation inflow regioncomprises a substrate.
 17. The injection laser of claim 1, wherein saidradiation inflow region is electrically conductive.
 18. The injectionlaser of claim 17, wherein an ohmic contact is formed with saidradiation inflow region.
 19. The injection laser of claim 1, wherein aportion of said radiation inflow region comprises a plurality of layersoriented parallel to said inner surface, said plurality of layerscomprising materials having different refractive indices.
 20. Theinjection laser of claim 1, wherein said radiation inflow region has anoptical loss factor α_(RIR) of no more than about 0.1 cm⁻¹.
 21. Theinjection laser of claim 1, wherein: said gain region is bounded at twoopposite ends by two side surfaces; at least one of said side surfacesis inclined at an angle with respect to said inner surface, said anglebeing identical to an angle formed between one of said adjacent opticalfacets with said inner surface; and said side surface has a reflectioncoefficient equal to that of said adjacent optical facet.
 22. Theinjection laser of claim 1, wherein said at least one optical facetcomprises one of said reflectors of said optical resonator and is formedsuch that said angle of inclination ψ is equal to the outflow angle φ,which is equal to arccos(n_(eff)/n_(RIR)).
 23. The injection laser ofclaim 1, wherein: said at least one optical facet is oriented such thatsaid angle of inclination ψ is equal to (π/4)−(φ/2) whereφ=arccos(n_(eff)/n_(RIR)); and at least part of said outer surface ofthe radiation inflow region that coincides with a projection of saidoptical facet formed thereon forms one of said reflectors of the opticalresonator.
 24. The injection laser of claim 1, wherein: said at leastone optical facet is oriented such that said angle of inclination ψ isequal to (π/4)+(φ/2), where φ=arccos(n_(eff)/n_(RIR)); and at least partof one surface of said injection laser opposite to said inflow regionthat coincides with a projection of said optical facet formed thereon,forms one of said reflectors of said optical resonator.
 25. Theinjection laser of claim 1, wherein one of said optical facets isoriented such that said angle of inclination ψ is equal to zero.
 26. Theinjection laser of claim 25, wherein said optical facet comprises areflective coating formed thereon.
 27. The injection laser of claim 1,wherein at least one of said reflectors of said optical resonatorcomprises an external reflector.
 28. The injection laser of claim 27,wherein said radiation inflow region comprises two optical facets eachoptical facet oriented such that said angle of inclination ψ withrespect to said plane perpendicular to said longitudinal gain axis isequal to zero.
 29. The injection laser of claim 28, wherein at least oneof said reflectors of said optical resonator comprises a cylindricalmirror.
 30. The injection laser of claim 27, wherein at least one ofsaid reflectors of said optical resonator comprises a plane mirror. 31.The injection laser of claim 27, wherein at least one of said reflectorsof said optical resonator comprises a diffraction grating.
 32. Theinjection laser of claims 1, wherein at least one of said reflectors ofsaid optical resonator comprises a spherical mirror.
 33. The injectionlaser of claim 1, comprising at least two gain regions each having alongitudinal gain axis and being disposed adjacent an inner surface ofat least one radiation inflow region.
 34. The injection laser of claim33, wherein an independent ohmic contact is formed with each of saidgain regions, each ohmic contact positioned opposite said radiationinflow region.
 35. The injection laser of claim 33, comprising at leasttwo sequences of gain regions and a common radiation inflow region foreach sequence of gain regions, each sequence of gain regions comprisingat least two gain regions, said longitudinal gain axis of each gainregion in each sequence being parallel to each other and being disposedat right angles to a line of intersection between active layers and anextension of a plane of an optical facet of said common radiation inflowregion.
 36. The injection laser of claim 35, further comprising ohmiccontacts adjoining strips of metallization for respective sequences ofgain regions, said strips of metallization formed on at least part ofthe outer surface of at least one of said common radiation inflowregions.
 37. The injection laser of claim 35, further comprisingindependent ohmic contacts formed with strips of metallization that arepositioned parallel to said gain axes of said gain regions and that areinsulated from each other, said strips of metallization being locatedopposite said radiation inflow region.
 38. The injection laser of claim35, wherein said gain regions are formed along at least one lineparallel to said longitudinal gain axes of the gain regions.
 39. Theinjection laser of claim 38, wherein: said radiation inflow region hasan outer surface and a thickness d_(RIR), said gain regions havingleading edges closest to one side of said heterostructure, said gainregions being separated by a distance equal to 2d_(RIR)/tan φ whenmeasured from respective leading edges of said gain regions; and atleast part of said outer surface coinciding with a projection of saidgain region onto it is optically reflective.
 40. The injection laser ofclaim 35, wherein: at least two adjacent gain regions are electricallyisolated by a nonconductive part of said radiation inflow region, andohmic contacts associated with each of said gain regions areelectrically coupled by a metallization layer.
 41. The injection laserof claim 1, further comprising at least two gain regions each havinglongitudinal gain axis and adapted to output light at identical outflowangles φ, said gain region formed on opposite surfaces of said radiationinflow region along two lines that are parallel to each other and tosaid longitudinal gain axes, said gain regions having leading edgesnearest to a common side of said heterostructure, said gain regions onopposite sides of the inflow region being separated by a distance ofd_(RIR)/sin φ when measured from said leading edges, where d_(min) isthe thickness of said radiation inflow.
 42. The injection laser of claim1, further comprising a semiconductor layer formed on said radiationinflow region, said semiconductor layer having a refractive index lessthan said effective refractive index n_(eff).
 43. The injection laser ofclaim 42, wherein said semiconductor layer has a refractive indexapproximately equal to n_(min).
 44. The injection laser of claim 1,wherein said radiation inflow region has a thickness d_(RIR) in a rangebetween about 2 and 100 micrometers.
 45. The injection laser of claim 1,wherein said at least one said gain region flares outward from a portionhaving a first width to a portion having a second width larger than saidfirst width.
 46. The injection laser of claim 1, wherein said at leastone gain region comprises at least three gain regions, said at leastthree gain regions including a middle gain region surrounded by firstand second end gain regions.
 47. The injection laser of claim 46,wherein one of said cladding layers is thicker along a portion adjacentsaid middle gain region than along portions adjacent said first andsecond end gain regions.
 48. The injection laser of claim 46, whereinboth of said cladding layers has a substantially identical thicknessalong said middle gain region and said first and second end gainregions.
 49. The injection laser of claim 46, wherein said ohmiccontacts comprise at at least a first ohmic contact associated with saidmiddle gain region, a second ohmic contact associated with said firstend gain region, and a third ohmic contact associated with said secondend gain region.
 50. The injection laser of claim 46, wherein said ohmiccontacts include one continuous ohmic contact associated with the middlegain regain and the first and second end gain regions.
 51. The injectionlaser of claim 46, wherein said radiation inflow region comprises arectangular parallelepiped.
 52. The injection laser of claim 46, furthercomprising a semiconductor layer having a refractive index less thansaid effective refractive index n_(eff) formed on said radiation inflowregion.
 53. The injection laser of claim 46, wherein said at least oneradiation inflow region comprises at least one radiation inflow regionon each of opposite sides of said active layer.
 54. The injection laserof claim 53, further comprising semiconductor layers having refractiveindices less than said effective refractive index n_(eff) formedadjacent each of said radiation inflow regions.